This invention relates to the use of electrogenerated bases as catalysts for the addition of organic electrophiles to carbon acids.
Electrochemical reduction of organic compounds often afford strongly basic and/or nucleophilic species, for example, carbanions, radical anions, dianions, and the like. The nucleophilic character of these species has been extensively exploited in many coupling, polymerization, displacement, and carboxylation reactions -- as reported, for example, in Organic Electrochemistry (Baizer, ed.) Marcel Dekker, New York, pp. 679-704; 947-974; Baizer et al, Journal of Organic Chemistry, 37, 1951 (1972); and Tysee, U.S. Pat. No. 3,945,896.
However, their basicity has been used in synthesis only to a limited extent. For example, the synthetic utilization of electrogenerated bases in the Wittig reaction, the Stevens rearrangement, and the Michael addition reaction has been described, respectively, in Iverson et al, Tetrahedron Letters, 3523 (1969), Iverson, Tetrahedron Letters, 55 (1971); and Baizer et al, Tetrahedron Letters, 5209 (1973).
The progress of synthetic utilization of electrogenerated bases has been impeded by the usual requirement that the electrogenerated base must be present in stoichiometric amounts, an unappealingly wasteful and expensive requirement. And even in those reactions where the electrogenerated base need be present in only catalytic amounts, for example, the Michael addition reaction noted hereinabove, the utility of such bases has been severely limited in that little, if any, advantage is demonstrated over corresponding chemical procedures. Moreover, when a portion of the reactants is converted to the electrogenerated base to serve as a catalyst, that portion of the reactant is "wasted " with respect to the product, thereby producing a lower maximum yield of product (unless such reactant is recovered and subsequently reused). Such a disadvantage is encountered in the electrogenerated base-catalyzed Michael addition reaction and Stevens rearrangement of the prior art.
An additional disadvantage of direct electroreduction of the reactants to the electrogenerated base and/or carbon acid anion is that higher than desirable cathode potentials are in general required, thereby increasing the possibility of side reactions to produce undesired by-products.
Furthermore, processes employing electrogenerated bases as catalysts in the addition of organic electrophiles to carbon acids have been glaringly unavailable, possibly because of the general expectation that such bases would successfully compete with the carbon acid anion for the available in situ organic electrophile, thereby producing little, if any, carbon acid-organic electrophile addition product.
These and other difficulties and disadvantages encountered in the prior art processes of synthetic utilization of electrogenerated bases are overcome by the discovery that the addition of organic electrophiles to carbon acids is conveniently accomplished via catalysis by electrogenerated base to yield the carbon acid-organic electrophile and addition product.